BERLIN, April 6 (Reuters) - Germany and France will launch a programme this month to develop a new marine patrol and surveillance aircraft, the German navy said on Friday, in what defence sources said was a response to a sharp increase in Russian submarine patrols.

German Defence Minister Ursula von der Leyen and her French counterpart, Florence Parly, plan to sign a letter of intent about the new “Maritime Airborne Warfare System” at the Berlin air show on April 27, it said on its website.

The two countries agreed last July to seek a “European solution” to replace existing marine surveillance planes, and develop a road map to that end by mid-2018. The letter of intent formalises those plans and paves the way for both countries to harmonise their military requirements for the maritime mission.

The initiative is part of a larger drive by France and Germany to increase their cooperation on defence programmes, including efforts to develop a new European fighter jet.

Germany now uses the P-3C Orion built by Lockheed Martin Corp to patrol large swathes of ocean for submarines and other potential threats, while France operates the Atlantique 2, or ATL2, produced by Dassault Aviation in the 1980s.

German navy officials were not immediately available for further comment on the programme, or how it will tie into an effort by eight NATO allies, including France and Germany, to cooperate on “multinational maritime multi-mission aircraft capabilities.” The programme also includes Canada, Poland, Italy, Spain, Turkey and Greece.

NATO members are modernising and upgrading military equipment in the wake of increasingly aggressive military actions by Russia, including a high level of submarine patrols not seen since the end of the Cold War.

In February, NATO Deputy Secretary General Rose Gottemoeller underscored the importance of replacing existing maritime patrol aircraft that will be retired between 2025 and 2035.

France and Germany will also take a “significant first step” on development of a new European fighter jet at the Berlin air show, France’s Parly told French media on Thursday.

In addition, they will display for the first time a life-sized model of the planned “Eurodrone,” a programme that also includes Italy and Spain.

Germany on Friday underscored its commitment to joint European weapons programmes, but said it also planned to take a more assertive approach in seeking waivers from European Union regulations to safeguard certain key defence technologies.

Defence Ministry spokesman Holger Neumann told a government news conference the step was part of a larger effort to improve Germany’s weapons buying system amid reports of persistent gaps in military equipment and personnel.